1. Field of the Invention
The present invention relates to a method of image formation using silver halide photosensitive elements and particularly to an improvement in adaptability to developing agents in image formation based on graphic art lithographic type silver halide photosensitive elements (hereinafter, referred to as lith-type photosensitive elements).
A lith-type photosensitive element, comprising a support having coated thereon silver halide photographic emulsions having a very high contrast characteristic, are processed with a special type of extremely high contrast developer (hereinafter referred to as a lith-type developer) to provide a very contrasty image comprising half-tone dots and lines, and are used as photographic originals for printing plates. A lith-type developer is an alkaline solution, a so-called "infectious developer" which conventionally contains a dihydroxybenzene type principal developing agent and, in addition, for example, an aldehyde-alkali metal bisulfite as a preservative. In the course of the development, the dihydroxybenzene derivatives are infectiously activated in turn and cause a rapid development, which results in a high contrast image being obtained.
In this type development, a long time is required until the start of blackening (in other words, the initial development in this type development is slow). On the contrary, since the contrast begins to reduce without a substantial change in the photographic density in the final development, this type development has a defect that the image quality, particularly the dot quality, is deteriorated.
It has been desired to accelerate the above-described initial development as quickly as possible and, in addition, to reduce the deterioration of the image quality at the final development so that the high sensitivity and a satisfactory image quality, particularly high contrast and high photographic density, can be always obtained over a wide range of developing times, i.e., from the initial development to the final development.
In addition, the image quality obtained in the step of development using a lith-type developer tends to depend on the degree or manner or agitation of the developing solution at development.
For example, in a manual method using a tray for development processing, the contrast, photographic sensitivity and dot quality of the image obtained are strongly influenced by changes in the time and strength of agitation of the developing solution.
In addition, there is usually a considerable difference in the image quality obtained due to a difference in the agitation between a manual method and a method using an automatic processor. Furthermore, the image quality obtained often varies according to the type of automatic processor, since there is also a difference in the method and strength of the agitation between different types of the processors. Moreover, commonly a developing solution is not always agitated uniformly even in the same automatic processor and there is also a difference in agitation between positions in the processor. In consequence, where a large size film is uniformly exposed to light through a half tone screen and then is subjected to development processing, the lack of uniformity of development due to the irregularity of agitation of the developing solution tends to occur in both the width and the length direction of the film. It has been desired to develop a method of image formation which is not as adversely affected by factors such as the agitation of the developing solution.
On the other hand, a lith-type developer is usually prepared by mixing a first solution primarily containing a principal developing agent and a second solution primarily containing an alkali agent just before the use of the developer. The pH of the developer thus-prepared varies according to a change in the mixing ratio of the first solution to the second solution as described above.
The change in pH of the lith-type developer (macroscopic pH change) seriously affects the photographic properties of the image obtained on development of a lith-type photosensitive element and consequently causes a change in photographic sensitivity and the like. Moreover, the photographic properties are considerably affected by a microscopic difference in pH during development between, for example, an exposed portion and an unexposed portion in the photosensitive element.
In view of the above, it has been desired to develop a method of image formation using a lith-type photosensitive element which is not as adversely affected by such a macroscopic and microscopic change in pH.
In addition, commonly in a system of processing a large amount of photosensitive elements with the same developing solution over long periods of time, the image quality obtained by development processing with a so-called "fatigued developer" is generally inferior to that obtained with a fresh developer at the beginning of development processing after the preparation thereof. It is common for the dot quality obtained using a fatigued developer of the lith-type after a mass processing with a lapse of a long time, in particular, to be quite inferior to that obtained with a fresh developer. In consequence, it has been desired to develop a method of image formation which provides an image quality with which no or reduced deterioration occurs using a fatigued developer, when compared to using a fresh developer.